In recent years, there is a social demand for the use of carbon-neutral resources. It is the last biopolymers remaining on the earth that polymers accumulated by metabolization in natural sources such as plants.
It is known as plant-derived biopolymers that natural rubber and balata, milky gum extracted from gutta-percha tree, native to tropical areas. Natural rubber is cis-isoprene rubber made from sap collected from the rubber tree. Balata is a trans-polyisoprenoid and used for the production of, for example, golf balls and dental care materials. Also, eucommia rubber, which is an eucommia-derived biopolymer, is a trans-polyisoprenoid. Attempts have been made to use a vulcanizated eucommia rubber for motorcycle tires and tubes, but industrial use thereof has not yet been attained.
Extraction from plant tissue with organic solvents or the like for elution has been conventionally and effectively used for extraction of an eucommia-derived biopolymer. For example, Patent Document 1 discloses a method for producing an eucommia rubber characterized by subjecting a starting eucommia to ethanol extraction followed by removing the extracting solvent, subjecting the solid residue to toluene extraction, and then concentrating toluene or evaporating it to dryness so as to yield crude eucommia rubber; and further allowing the crude eucommia rubber to precipitate in a mixed solvent of toluene and methanol, dissolving the resulting precipitate in hot n-hexane, and then reprecipitating it by cooling. However, there are various disadvantages in this method, such as costs due to the use of organic solvents and thermal energy, an environmental burden due to the use of organic solvents, a continuous operation for a long period of time, and difficulties in scale-up. Furthermore, the resulting eucommia rubber merely contains rubber soluble in the extracting solvents, and has a decreased molecular weight.                [Patent Document 1] Japanese Laid-Open Patent Publication No. 2004-189953        
It is an object of the present invention to provide a novel biopolymer derived from natural sources, and a method for producing the same.